Formations of Active Species and By-Products in Water by Pulsed High-Voltage Discharge

Abstract

Formations of active species and by-products are different from bubbling different gases in a pulsed high-voltage discharge reactor. The identification of all the products and the formation rate determination of active species are quite important as the process is applied to wastewater disposal. Serials of measurements were conducted to do the identifications and determinations in this paper. Amounts of Á OH all increased but that of H 2 O 2 all decreased by bubbling gas. The Á OH formation rate was 3.49 · 10 À7 , 3.56 · 10 À7 , 3.21 · 10 À7 and 1.94 · 10 À7 mol l À1 s À1 with bubbling nitrogen, argon, air and oxygen respectively, but it was 1.61 · 10 À7 mol s À1 l À1 without bubbling. Without any bubbling, the H 2 O 2 formation rate was up to 6.53 · 10 À6 mol l À1 s À1 , while it was 9.97 · 10 À7 , 1.663 · 10 À7 , 1.73 · 10 À6 and 3.14 · 10 À6 mol l À1 s À1 with bubbling nitrogen, argon, air and oxygen, respectively. NO 2 À and NO 3 À was detected in discharged water with bubbling nitrogenous gas. Their formation made the pH decreased.

The Effects of Gas Composition on Active Species and Byproducts Formation in Gas–Water Gliding Arc Discharge

“…Experiments with air and oxygen had a tendency to corrode the electrodes to a greater extent than the other cases, and the results were in accordance with previous report [10]. The • OH and H 2 O 2 were formed through the excitation and/or ionization of the water molecules by the energetic electrons [11]:…”

“…Because the gas flow was mixed with water, the excited species could be trapped immediately by the water molecules [11]:…”

“…3d shows the N 2 + radicals are present during gas-water gliding arc discharge. Therefore, nitrogen oxides may be formed from the reactions of dissociated nitrogen and water [11,17]. …”

Water Purification by Plasmas: Which Reactors are Most Energy Efficient?

“…Oxygen formed by the action of the discharges can account for • O and O 3 , observed under spark discharges in water in the absence of externally supplied oxygen [48], by the following reactions Table 1) It is clear that if oxygen is bubbled into the discharge zone, it will provide reactants for production of reactive species, like • O and O 3 , in addition to • OH and H 2 O 2 [1,51,52]. Since oxygen and water molecules compete with each other for production of O 3 and H 2 O 2 , respectively, oxygen bubbling into the discharges zone results in a reduction of H 2 O 2 yield [52]. However, O 3 dissolved in water converts into • OH through a series of reactions [2].…”

“…However, O 3 dissolved in water converts into • OH through a series of reactions [2]. Therefore, • OH yield increases upon bubbling oxygen [52]. Bubbling of nitrogen and argon also increased • OH yield [52], although these gases cannot produce O 3 .…”